1. Field of the Invention
The present invention relates generally to an inspection system, and in particular to a baggage inspection system for detecting explosives using computed tomography (CT) and quadrupole resonance (QR) sensors.
2. Discussion of the Related Art
Over the years, baggage inspection systems have evolved from simple X-ray imaging systems that were completely dependent on interpretation by an operator to more sophisticated systems that can automatically recognize certain types of contraband. Some systems employ single energy or dual energy X-ray radiation transmitted through or scattered from examined baggage. Some systems use a single view detector arrangement, while other systems utilize dual-view or multi-view arrangements. Single or dual-view systems usually scan baggage as it moves on a conveyor using a fan beam or a scanning pencil beam of X-rays in a fixed geometry. Multi-view CT sensors, on the other hand, usually scan stationary or moving baggage in a fixed geometry of scan angles and process data corresponding to the absorption of X-rays to reconstruct selected slices of the baggage.
In general, performance of explosives detection systems is measured using three primary parameters: false alarm rate, probability of detection, and scanning speed (throughput). Often, the improvement of one parameter is at the expense of the other parameters. For example, an increase in throughput may result in the undesirable effect of an increased false alarm rate or reduced probability of detection.
Although many CT based systems exhibit an excellent probability of detection, these systems are susceptible to high false alarm rates. A common reason for the generation of a false alarm is that conventional CT sensors have difficulty in distinguishing actual threat objects from harmless objects since these objects may exhibit similar threat definitions (for example, similar density and mass). Although there has been continued effort to improve false alarm rates of explosives detection systems employing CT technologies, for example, improvement is still needed.